An oxide photocatalyst (hereinafter referred to as a “photocatalyst”) including titanium oxide as a typical example generates electrons at a conductor by photoexcitation, when it is irradiated with light at a wavelength of energy not less than its band gap. The oxide photocatalyst then generates holes in a balance band, so that it expresses a photocatalytic function. Thus, organic matter or nitrogen oxides, which come into contact with a photocatalyst, are decomposed into water or carbon dioxide gas by the strong reduction power of the electrons or the strong oxidative power of the holes. Accordingly, a photocatalyst has functions such as anti-fouling, deodorization or anti-bacterial properties. Environmental purification methods or devices, which utilize the anti-fouling, deodorizing and anti-bacterial functions of a photocatalyst, have become a focus of attention. In order to achieve the high performance and high efficiency of the photocatalyst, it is desired to enhance the photocatalytic activity of the photocatalyst itself.
Since the conventional photocatalyst material is generally used in a powdered state, it is extremely difficult to treat it, and accordingly, it is difficult to incorporate it into an environmental purification device. In order to fix a powder photocatalyst, there is a method which involves mixing a power photocatalyst with an organic binder, applying the mixture onto a substrate, and fixing it under ordinary temperature or by heating. However, this method has a disadvantage in that since the organic matter covers a small or large part of the surface of a photocatalyst, the photocatalytic function of the mixture significantly decreases as compared with that of the original powder photocatalyst. In addition, this method has another disadvantage in that since the organic binder as an organic matter is decomposed by the photocatalytic function, coating strength deteriorates, and powders thereby gradually fall away. The disadvantage regarding the detachment of powders has been overcome by the solidification of the powder photocatalyst with an inorganic binder. However, since the binder covers a part of the photocatalyst, the surface area that can be effectively used for the expression of the photocatalytic function decreases. Thus, the problem regarding the significant decrease of the photocatalytic function has not been overcome.
In order to solve the above problem of a powder photocatalyst, a large number of techniques for producing a photocatalyst such as the sol-gel method disclosed in Japanese Patent Laid-Open No. 10-180118 and others have been proposed in the past. Attempts have been made to solve the above described problems regarding a powder oxide photocatalyst and to improve its photocatalytic function. However, the satisfactory achievement of a high activity has not yet been obtained.
It is the object of the present invention to solve the problems of the above prior art techniques and to provide a photocatalyst material that can be used to achieve a photocatalyst with an excellent ability to adhere to a substrate as well as a high photocatalytic activity, and a production method thereof.